Common dayflower is an herbaceous annual plant that sprawls along the ground like a vine, often rooting at the nodes. Flowers last for only a day, emerging from a boatlike sheath, one at a time. There are 3 petals: 2 large blue petals above, plus 1 much smaller white or greenish-white petal below. There are 6 stamens (the male parts): 3 on short stems are sterile (these are called staminodes), and 3 on longer stems produce pollen. Blooms May-October. Leaves alternate, clasping the stem, narrowly ovate to lance-shaped.
Similar species: There are 4 more dayflowers in the genus Commelina recorded in Missouri. They have similar characteristics.